Molded records, such as conventional audio records and the more recently developed video records, are manufactured by the same general procedures. The initial step in the procedures is to record the signal information desired to be molded into the records onto a magnetic tape. The magnetic tape is then used to control a cutting tool which cuts a spiral groove into an appropriate substrate. The spiral groove is cut with surface relief patterns on either the side walls or the base of the grooves which correspond to the information desired to be molded into the final record.
Once the recorded substrate is obtained, it is used as a pattern from which to make a series of parts referred to as masters, molds, and stampers. The initial step is the preparation of the masters. The masters are made by electroforming a metal, such as nickel or silver, onto the recorded grooved surface of the recorded substrate. Once a sufficient amount of metal is electroformed on the recorded substrate to make the self-supporting part, which typically is about 7 mils (0.0175 centimeter) of metal, the electroformed master is stripped from the recording substrate. The master which is thus obtained will be a negative image of the recorded substrate.
The grooved surface of the master is then used as a matrix on which to form a series of replicas referred to as molds. The molds are made by electroforming a metal such as nickel onto the master until sufficient metal has been deposited to make a self-sustaining part, which typically is about 7 mils (0.0175 centimeter) in thickness. From a given master a number of molds will be made. The resulting molds will be positive copies of the recording substrates and negative copies of the master.
Each of the molds is then in turn used as a matrix on which to electroform a series of parts referred to as stampers. The stampers are also formed from a metal such as nickel and are generally about 5 mils (0.0129 centimeter) in thickness. Stampers are negative copies of the original recorded substrate. It is the stamper which will eventually be used as the molding surface with which to press the surface relief pattern into the molded records.
In the manufacture of molded records, it is extremely important to "fan out" from the starting master to form a plurality of molds and then fan out from the molds to form a plurality of stampers. The cutting of the recording into the substrate is a relatively costly and time consuming step. If each of the stampers had to be made directly on a recorded substrate, the cost of the records would be extremely high. In addition, the ability to fan out from a given master to produce, for example 40 or 50 stampers, improves the uniformity from record to record of the recordings which are pressed.
Considerable problems are, however, encountered in the replication process used to form the molds and stampers from the masters. As noted above, the required parts are prepared by electroforming metal on the masters to form the molds and then on the resulting molds to form the stampers. In the electroforming process, the matrix to be replicated is attached to a cathode head and then immersed in an electroplating bath. A current is passed through the matrix to be replicated, which causes the metal from the electroplating bath to be deposited on the matrix and form the replica. Ideally, the metal should be deposited in a uniform thickness on the matrix without adversely affecting the matrix. In actual practice, however, substantial problems are encountered which result in formation of poor replicas having non-uniform plating and areas of high crystallinity, a condition referred to a "treeing". An even more serious problem, however, is encountered which is referred to as "burn outs". A burn out occurs when, apparently due to poor electrical contact, the matrix and the part to be formed on the matrix are heated up and eventually melt down or burn out. The burn out of the parts results in destroying both the matrix and the part formed on the matrix. If the matrix part is a master, it can be seen that this causes serious problems as it both destroys the part and eliminates the fan out production of parts from the master. If a mold is destroyed as a result of burn out, the amount of stampers which can be made is reduced because of the destruction of the mold.
A still further problem encountered in the electroplating process is referred to as "back plating" wherein the electrolyte leaks to the back of a matrix being replicated and deposits on the back rather than the face of the matrix. This damages the matrix and may also contribute to the burn out problems.
One of the most important pieces of apparatus used in the matrixing process is the cathode head. The cathode head is the apparatus on which the matrix to be duplicated is mounted for the electroforming process. The cathode head typically used in the prior art has a case or support made of a dielectric material, such as rubber or a non-conductive plastic, on which the matrix is mounted with electrical contact being made at the centermost portion of the matrix to the cathode of the electroplating apparatus.
It is also suggested in the prior art to use cathode heads having rubber backs and internal edge shields to hold the matrix to the cathode during electroforming. Such a combination of cathode head and edge shield is disclosed by L. R. Porratta et al. in U.S. Pat. No. 3,414,502, issued Dec. 3, 1968, entitled ELECTROPLATING APPARATUS FOR USE WITH A PHONOGRAPH RECORD MATRIX. Apparatus such as that disclosed by L. R. Porratta et al. has disadvantages in that they tend to allow leakage of electrolyte about the edges of the matrix to the back side of the matrix which is a highly undesirable condition, and burn outs are frequently encountered with this type of apparatus.
It is also suggested in the prior art that resilient edge shields be placed around the outer edges of the matrix before starting plating of the matrix. However, the prior art rubber edge shields are at best only marginally satisfactory when the shields are relatively new. When the edge shields are new and are applied correctly by skilled operators, reasonably satisfactory results can be obtained with regard to preventing electrolyte leakage. However, after the edge shields are used a few times, they tend to stretch and allow leakage of electrolyte. Furthermore, if the operators are not careful and do not apply the shields correctly, a substantial amount of leakage of electrolyte does occur about the outer edges of the shield resulting in undesirable back plating and possibly burn outs.
Another device suggested in the prior art to improve the quality of plating when making molds and stampers and the like for the manufacture of records is disclosed by Whitehurst in U.S. Pat. No. 4,259,166, issued Mar. 31, 1980, entitled SHIELD FOR PLATING SUBSTRATES. Whitehurst provides a masking apparatus which has certain distinct advantages over the prior art, but still has the disadvantage that it is both difficult to assemble and sometimes problems are still encountered in separating the electroformed part from the matrix, and burn outs are often encountered during manufacture of parts on the cathode head.
An additional improved apparatus for use in electroforming record matrixes is disclosed in the co-pending application by Prusak et al. in U.S. patent application Ser. No. 231,266, filed Feb. 3, 1981, now U.S. Pat. No. 4,341,613, entitled APPARATUS FOR ELECTROPLATING. The apparatus disclosed by Prusak et al. is a cathode head assembly including an outer ring member and seals which improve the quality of the electroforming parts formed on the apparatus. The apparatus disclosed by Prusak et al. has proven to be a significant improvement in the electroforming art with regard to preventing leakage of electrolyte to the back surface of the matrix and for providing replicas which can easily be separated from a matrix. However, the cathode head which is disclosed by Prusak et al., while a substantial improvement, still is not completely satisfactory and a considerable amount of burn outs are still encountered with this type of apparatus. What would be highly desirable would be a cathode head which would be easy to assemble and which when used in the electroforming operation would produce high-quality replicas which are easy to separate from the matrix and which would prevent leakage of the electrolyte to the back of the matrixes and which would eliminate the burn out problems during electroforming.